1. Sharp resonance of multimode periodic waveguide open resonator defined in SOI Ph.D student: Nikolay Piskunov Supervisor: Henri Benisty Institut d’Optique Graduate School, Laboratoire Charles Fabry, Palaiseau, 91127, France Acknowledgement: IMEC/EpixFab P.Dumon EDOM 2011, 07-08 March 1

2. Outline  Broad wg resonators  Theory  critical coupling  Realisation  SoI (EpixFab)   Measurement first results Overall scope : nonlinear optics in structured materials and "on-chip" resonators 2

3. Resonators & open resonators Fabry-Perot microring(s)/ CROW access/exit guide ~ Gaussian beam Single mode PhC wg...microtores Delicate coupling Broad waveguide resonator H. Benisty, Photon. Nanostruct. Fundam. Applic., 7, 115 (2009). 3

4. Broad waveguides : minigap clusters Dielectric wgSingle-side corrugated wg Modes interaction Regions: aligned gaps kzkz normalized freq. a/ Brillouin zone edge 4 Free Spectral Range 0 0 1 0.5 0 π/a

5. Critical mode coupling Bunch of modes shaped into very flat bands Light does several local round-trips at each bounce v g ~ 0 far around band edge Large finesse and high Q-factor of resonator,  Fabry-Perot, but opened. 5

6. h T4 Order m =50 w=5 μm Order m =75 w=7.5 μm a=384 nm h/a= 2.75, 3.00, 3.25, 3.50, 4.00 Realisation on SoI (EpixFab, IMEC) wg width Grating couplers : near-vertical coupling In our case : Lens coupling (50 mm) SoI neff (TE)  2.80 slow light 6 Grating in T6 T8 w W-h Modeling TARGET Grating out Dif. length of device

7. 7 FDTD simulation based on SEM picture Predicted target (triangular shape) Sample best result “bottle shape” Critical Coupling Region Peak Q Results are presented in log scale! Normalized Frequency, a/λ Normalized depth, h/a 5 4.5 4 2 Region of h/a values in exp. devices PhotonDesign software was used

8. IN out about 500 µ 30 µm grating coupler OUT grating coupler EpixFab sample (Pieter Dumon, Ghent) 6 mm h/  ~3.00 Device overview

9. Spectra T(l) acquired by triggered 2D- camera + image analysis Wavelength, nm Y-Pixel number Intensity transmission spectra obtained from Y –  image anlaysis to discard spurious signals from nearby wg's at  y  fieldsimulation 10 µm actual SEM image Tunable laser 2D camera Trig T4 DEVICE Grating out Grating in captSept17_T8_m50_1100uWF_hoa350_18ms_ 1520153015401550156015701580 45 50 55 60 1520153015401550156015701580 -0.05 0 0.05 0.1 0.15 0.2 9 Y 20 pixels 1520 1580

10. Analyzing m=50 T4 waveguides 1520153015401550156015701580 0 0.5 1 1.5 2 2.5 3 x4 x2 h/a=4 h/a=3.5 h/a=3.25 h/a=3 h/a=2.75 Q= 300 Q>1000 10 Transmission (shifted), arb.un. Single FP Wavelength, nm FSR Theory: λ/m=31 nm (no dispersion) Exp: 25 nm (n group ~1.2 n phase )

11. 1520153015401550156015701580 0 0.5 1 1.5 2 2.5 3.5 x1.5 x2 Analyzing m=50 T8 waveguides h/a=4 h/a=3.5 h/a=3.25 h/a=3 h/a=2.75 Q=750 Q=4000 11 Triple FP resonator behavior Wavelength, nm Exp. FSR 26 nm Transmission (shifted), arb.un.

12. Comparison between experimental and calculated results 12 ++++ +-+- Double FP resonator FSR Calculation was performed using transfer matrices method taking into account wg’s dispersion Width 7.5 nm FSR ~ 15 nm

13. Nonlinear effects in corrugated waveguides Self-phase modulation (SPM) - process of phase-change of pulse propagating in the medium with nonlinear refractive index Δφ=n 2 ω 0 /c*I 0 *L Δφ>2π Photon energy SignalPumpIdler Optical Parametric Oscillator … & dispersion Even spacing Uneven spacing Q~4000 Finesse f=Q/m=80 Enhancement ~f 2 around 65000 I 0 ~10 7 J/cm 2

14. Conclusion  "Critical coupling" applied to SoI structure  Good in/out coupling maintained at high Q  Periodic waveguide looks like multiple FP  Promising for NLO (SPM&OPO)  Q ~4000 attained (measurements still ongoing) 14

15. Thank you for attention! 15

16. Questions 152015301540155015601570 1580 0 0.5 1 1.5 2 2.5 3 x4 x2 16

17. 152015301540155015601570 1580 0 0.5 1 1.5 2 2.5 3 x4 x2 Questions 17